1. Field of the Invention
The present invention relates to a configuration of a diaphragm for a speaker device preferably usable for a mobile phone.
2. Description of Related Art
Conventionally, there is known a dome-shaped speaker including a dome-shaped diaphragm having a voice coil form having a U-shaped cross-section (see Japanese Patent Application Laid-open under No. 5-30592 (p. 5, FIG. 6), which is referred to as “Reference-1” hereinafter).
In the dome-shaped speaker disclosed in Reference-1, since the voice coil is arranged in the voice coil form having the U-shaped cross-section, the driving force of the voice coil directly operates on the voice coil form at the time of sound reproduction. Therefore, the strength capable of enduring the driving force of the voice coil is necessary for the voice coil form. In this point, since the voice coil form is formed into a circular or track shape and an annular shape, it can be said that the strength is comparatively ensured in the voice coil form in consideration of the configuration.
Meanwhile, there is known a speaker formed into an elongated shape in comparison with the dome-shaped speaker (see Japanese Patent Application Laid-open under No. 11-187484, which is referred to as “Reference-2” hereinafter).
In the speaker according to Reference-2, the voice coil is formed into a flat-plate shape, and a central part of the diaphragm having a recessed cross-section is connected to an upper coil being a component of the voice coil. Thereby, at the time of sound reproduction, the driving force of the voice coil is transmitted to the diaphragm itself via the central part of the diaphragm.
However, in the speaker device according to Reference-2, since the central part of the diaphragm has the elongated configuration to be formed into a linear shape, the strength of the part is structurally smaller than that of the circular voice coil form of the diaphragm disclosed in Reference-1. Thus, at the time of the sound reproduction, the central part of the diaphragm is bent, or the central part of the diaphragm rolls. Then, it may happen that, in the magnetic gap, the central part of the diaphragm and the magnetic circuit contact or collide and an abnormal sound occurs.
In this point, in the speaker device, a damper is provided at a position on a side opposite to the diaphragm with sandwiching the voice coil, and the central part of the damper is connected to a lower part coil of the voice coil. Thereby, the strength of the supporting part of the voice coil is ensured to some extent, and such a problem hardly happens. Namely, in the speaker having the elongated configuration, the strength of the supporting part of the voice coil is ensured to some extent by providing the damper, and the above problem hardly happens.